R-T-B based sintered magnets have a high saturation magnetic flux density, and thus are advantageous for achieving downsizing and high efficiency of using equipment and are used for voice coil motors of hard disk drive, motors for various industries, drive motors of hybrid vehicle, and the like. In applying the R-T-B based sintered magnets to the hybrid vehicles or so, the magnets are exposed to a comparatively high temperature, and it is thus particularly important to prevent thermal demagnetization due to heat. To prevent this thermal demagnetization, it is well known that a method for sufficiently enhancing coercivity at room temperature of the R-T-B based sintered magnets is effective.
For example, a method for substituting a part of Nd of an Nd2Fe14B compound of main phase for heavy rare earth elements, such as Dy and Tb, is known as a method for enhancing coercivity at room temperature of Nd—Fe—B based sintered magnets. For example, Patent Literature 1 discloses a technique for substituting a part of Nd for heavy rare earth elements so as to sufficiently enhance coercivity at room temperature.
Patent Literature 2 discloses a technique for increasing a concentration of heavy rare earth elements only in shell part of a main phase so as to achieve high coercivity with less amount of heavy rare earth elements and prevent decrease in residual magnetic flux density to some degree.
It is pointed out that prevention of magnetic domain wall motion of a reverse magnetic domain generated is also important for improvement in coercivity of rare earth magnets. For example, Patent Literature 3 discloses a technique for improving coercivity by forming fine magnetic hardening products of non-magnetic phase in grains of main phase R2T14B and thereby pinning magnetic domain wall.
Patent Literature 4 discloses a technique for preventing magnetic domain wall motion and improving coercivity by forming a part in main phase grains. In this part, magnetic properties have been changed from those of main phase.